Support is requested for years 16 through 20 of a program to train graduate students and postdoctoral fellows at Stanford University School of Medicine in the Molecular Basis of Host-Parasite Interaction. This training program crosses the disciplines of infectious disease, molecular biology, genetics, cell biology, biochemistry, immunology and microbiology in the area of microbial pathogenesis and the host native and acquired immune responses. The successful training record of our faculty, including the predoctoral and postdoctoral students trained over the past 14 years of this program, supports the continuation in the next period. The support provided by this training grant has fostered the establishment of the Host-Parasite training program at Stanford, allowing highly qualified individuals to train in the program, and has precipitated a range of interactions among the various faculty members. In a modestly sized program, highly regarded scientists who investigate innate and acquired immune responses, in MHC class I variability and T cell recognition, interact daily with experts in the genetics, cell biology and biochemistry of viruses, bacteria and eukaryotic parasites. The training program is based in the Department of Microbiology and Immunology, but includes faculty members chosen by students in the program from outside the Department. Faculty expertise in immunology and a wide range of microbiological topics are available to students and postdoctoral fellows in the program. Interactive seminar series, departmental retreats and journal clubs are in place to assure scientific exchange across traditional disciplines. Trainees from underrepresented minorities are well represented, as are female trainees. As a result of altered enrollment and recruitment policies in biosciences at Stanford, the program is enjoying even greater interest and increased quality of applications. Eight predoctoral and four postdoctoral training slots are requested for the continuation of this program.